Document Type : Research Paper
Authors
1
Department of Geology, Petrology and Economics, Faculty of Earth Sciences, Shahrood University of Technology, Haft Tir Square, Shahrood City, Semnan Province
2
Semnan, Shahrood, University Boulevard - Shahrood University of Technology - Faculty of Earth Sciences - Department of Petrology and Economic Geology. Dr. Mahmoud Sadeghian
3
Department of Mineralogy-Petrology-Economic Geology, School of Geology, Aristotle University of Thessaloniki (AUTh), Greece
4
Institute of Geology and Geophysics, Chinese Academy of Sciences (CAS), China,beijing.
5
Institute of Geology and Geophysics, Chinese Academy of Sciences (CAS), China,Beijing
Abstract
The study area is located in the N-NE Bafq and the central Iran structural zone. The Rizu-Desu volcano-sedimentary sequence is crosscut by bimodal (basic and felsic) intrusions and dikes, with compositions ranging from monzogabbro to leucogranite. In the monzogabbro-monzodiorite intrusions (540 to 520 Ma) of the investigated region, plagioclase (with a dominant albite-oligoclase composition), pyroxene (diopside and augite), Ca-Fe-Ti-rich amphiboles (magnesiohornblende, tschermakite, Kaersutite, and ferrokaersutite), and biotite (Fe-biotite and Mg-biotite, and also Ti-rich (0.38-1)) are the essential minerals. Apatite, monazite, magnetite, titanomagnetite, titanite (sphene), and zircon are also accessory minerals. Geothermobarometry investigations based on the mineral chemistry of pyroxene, amphibole, and biotite indicate the temperatures of cessation of exchange and final equilibrium of the minerals, mainly covering a temperature range of 1270 to 1140 °C (pyroxenes), 890-790 °C (amphiboles) and 780-745 °C (biotites) (in respectively) and the pressure mainly cover range of 12.33 to 0.5 kbar. Petrological features of the studied rocks are very similar to those of appinite rocks. The parental magmas of monzogabbro-monzodiorite intrusions have mostly an alkaline nature and originated from partial melting of the metasomatized mantle source in an intracontinental rift tectonic setting. The resulting magmas evolved by fractional crystallization, and possibly crustal contamination, then emplaced in the continental crust around the Ediacaran-Cambrian boundary.
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